[JoeyPBasically]

So I took my accuracy systems inc armalite style upper out yesterday to the range. After 100ish rounds I found 3 pierced primers. I was shooting 7.62x51 175 gr lake city mil surp. I. Have enclosed some pictures to show you all what I'm dealing with. Put a call in to ASI and waiting for the boss to call me back on Wednesday as he is out of the office until then. Any ideas?

 

[JoeyPBasically]

First pic pic here is debris cleared out of the firing pin port, so may have had what looks like 3-5 but I found 3 casing pierced.

 

[ratula]

what kind of trigger is in it? Is the AR10 completely stock?

 

[JoeyPBasically]

I built the lower with an iron ridge billet lower and a national match armalite lower parts kit, the upper was completely built by ASI. The entire rifle is custom for the most part. What effect would the trigger have on this?

 

[dsdmmat]

My initial guess is it is the ammo. After looking at the pictures of the cases it seems they are showing pressure signs, the really shined mark where the ejector imprinted itself. Try to shoot some Other commercial ammo and see if it still does it. Some Federal Gold Metal match 168 stuff if you can fins any.

 

[RandallOfLegend]

I agree with dsdmmat. The firing pin is not piercing the primer. You are having overpressure causing the primer to flow around the firing pin. You can see the ejector imprinting on the back end of the brass. I would buy some factory ammo and do some shooting to see if the problem moves WITH the gun or with the ammo.

 

[JoeyPBasically]

The firing pin definetly needs replacing at this point though no?

 

[VARMINT223]

How cleaned/lubed is the carrier group? Is the firing pin free floating or does it hang up and stick? Does the firing pin movement seem sluggish? Is the firing pin bent along the overall length? Any slam fires?

 

[JoeyPBasically]

How cleaned/lubed is the carrier group? Is the firing pin free floating or does it hang up and stick? Does the firing pin movement seem sluggish? Is the firing pin bent along the overall length? Any slam fires?

Very clean and frog lubed, the pin started free floating but as the pierces happened, primer pieces went into the firing pin port making it slow down. Had 2 no fires, no slam fires or pre detonations.
firing pin seems to have a nick in it, I tried to get a good picture of it above.

 

[meketrefe]

you have two factors. A) hot ammo. B) Potentially a firing pin protruding in excess that should not be less than 0.025" or more than 0.035".
you can check this with a caliper or gauge. Make sure everything is super clean to measure w/o debirs.
If this is the problem it is easy to fix. You just need to very slowly remove the excess.

 

[Twogunwilly]

Looks like a bunch of cosmoline in there to me, not saying that's the problem but....

 

[Benellinut]

I highly doubt that LC ammo is over pressured, first thing I'd do is have the headspace checked.

 

[Benellinut]

Very clean and frog lubed, the pin started free floating but as the pierces happened, primer pieces went into the firing pin port making it slow down. Had 2 no fires, no slam fires or pre detonations.
firing pin seems to have a nick in it, I tried to get a good picture of it above.

Two no fires and some with pierced primers, both signs of too much headspace. Could be other things but those two combined from the same ammo in one outing with a new rifle would lead me to at least check the headspace.

 

[ratula]

I built the lower with an iron ridge billet lower and a national match armalite lower parts kit, the upper was completely built by ASI. The entire rifle is custom for the most part. What effect would the trigger have on this?

imney
I would like to know what kind of trigger, 2 stage ? I had a similar problem after I put a Timney in a similar rifle, the firing pin was blastic thru the primer caps, and another rifle the primers were not getting hit hard enough.I put the stock trigger back in and had no more problems. you may want to change the firing pin first......Also try using different ammo and see what happens although military primers are much harder than civilian.

 

[Benellinut]

You also need to clean out all that lube, way too much and it may be making it's way into the chamber. Make damn sure it's not getting into the chamber, the chamber should be free of all lube. You've got a lot of little pieces of brass that's sticking to the lube, see the chunks stuck to the face of your bolt? Probably also inside the barrel extension around the locking lugs that you can't see, I'd get a lug cleaning tool to clean the extension out, like this --> http://www.brownells.com/gun-cleani...r-15-and-ar-10-lug-recess-tool-prod34907.aspx

I've got one of those (new) for the AR10 I'd cut you a deal on, you'll have to buy the cotton rolls, I only have a few.

 

[JoeyPBasically]

imney
I would like to know what kind of trigger, 2 stage ? I had a similar problem after I put a Timney in a similar rifle, the firing pin was blastic thru the primer caps, and another rifle the primers were not getting hit hard enough.I put the stock trigger back in and had no more problems. you may want to change the firing pin first......Also try using different ammo and see what happens although military primers are much harder than civilian.

It's an armalite national match parts kit and trigger.

 

[meketrefe]

I highly doubt that LC ammo is over pressured, first thing I'd do is have the headspace checked.

Why would anyone think they are over-pressure? They are hot military loads as per the Lake City NATO head stamp.

If the op can check the side of the cases looking some stretching then it is a sign but primers look fine other than the piercing.
Always chamber clean and dry of oil and debris. Also specially important to use gauges and measure.
Also if you had two misfires can you check the primers and cases? Compare a round from this batch with one fired. With the calipers
is easy measuring and take a delta reading from the datum (shoulder) of the case. If you do not have a gauge use a larger case caliber and compare.
If you have a HS gauge go and do the no go headspace although an Armalite factory rifle should be fine.
All things have to check ok. Don't discard this could be an ammo issue with the surplus.

 

[JoeyPBasically]

This is a custom built rifle, not a stock armalite. Only thing made by armalite on this rifle is the stripped upper receiver and the lower parts kit. The upper was made by Accuracy Systems Inc. I built the lower using an iron ridge billet lower and a armalite national match grade parts kit. I don't think frog lube would cause pierced primers. I have a feeling my gun either doesn't like this ammo, the firing pin/port is off, or possibly the headspace. But I feel like a headspace issue would of cause far more problems.

 

[JoeyPBasically]

The cases didn't appear to have any stress marks on the sides.
also thank you everyone for your input so far! I really appreciate it. Nothing more stressful than when your expensive rifle fails. Rifle isn't brand new but has only been taken out 4-5 time with a maximum round count of 400 through it.

 

[meketrefe]

This is a custom built rifle, not a stock armalite. Only thing made by armalite on this rifle is the stripped upper receiver and the lower parts kit. The upper was made by Accuracy Systems Inc. I built the lower using an iron ridge billet lower and a armalite national match grade parts kit. I don't think frog lube would cause pierced primers. I have a feeling my gun either doesn't like this ammo, the firing pin/port is off, or possibly the headspace. But I feel like a headspace issue would of cause far more problems.

You welcome. This is our job to see if we can help each other.
The headspace in 7.62x51 has larger tolerances and even if it was on the large side the brass is designed to take it w/o any issues.
The only problem here is with very old military chambers like found in surplus FAL and even some early M14's / M1A converted that some folks found didn't pass the field gauge check or otherwise found out the hard way if you know what i mean.
Also an upper built by Accuracy Ssytem shoud be dead on. I mean you can try for your own peace of mind but I am sure that is not
the problem. however measure the firing pin protrusion and don't discard the ammo problems. I had batches of expensive Match Ammo
factory new blowing off primers. so imagine military surplus. Something very rare but it happends.
Again measure the protrusion.